Angiogenesis is an essential life process by which new blood vessels are formed in response to normal tissue development. The continuous growth of blood vessels or neovascularization provides increased blood circulation throughout various regions of the body. The ability for blood vessels to successfully perform their circulatory function is dependent upon either the existence of relatively unobstructed passageways, or the regeneration or neoformation of new blood vessels. In the past, there has been significant interest in maintaining an adequate blood supply to tissues by removing obstructive material in existing vessels. Many devices and drug therapies have been developed in an effort to eliminate the accumulation of plaque deposited on arterial walls in what is commonly referred to as arteriosclerosis. At the same time, revascularization and the creation of new blood vessels support the changing circulatory needs of the body. It has been observed that neovascularity may be generally achieved in either an artificially induced manner or as a spontaneous bodily reaction. For example, with respect to coronary applications, transmyocardial revascularization has been available for numerous patients in the past when coronary artery bypass grafting procedures were not an available option. During transmyocardial revascularization, multiple channels are generally formed directly in the myocardium to provide ischemic myocardial regions direct access to a source of oxygenated blood. These channels may be formed externally through the epicardial wall with instruments such as laser devices during open chest procedures, or openings may be created percutaneously with devices that access a heart chamber such as the left ventricular endocardium. Various laser apparatus and procedures have been developed to perform these artificially induced neovascularization techniques particularly for end stage coronary artery disease. The patency and effectiveness of these small channels or micro-channels is still being investigated as to the importance of their ability to remain open despite scarring and ensuing fibrosis. The therapeutic benefits and overall effects from these revascularization procedures have not been established with substantial certainty.
The study of angiogenesis and the spontaneous growth of new blood vessels has been studied in depth for many years. Although numerous angiogenic factors have been identified, the precise mechanism by which the body creates new blood vessels is not fully understood. It has been observed that trace amounts of some angiogenic factors exist in normal tissue, but they fail to demonstrate significant angiogenic activity other than in the ordinary growth and development of tissues and organs. In addition, a variety of growth factors and vasoconstrictors demonstrate an ability to promote neovascularization by induced angiogenesis when injected into body regions such as the ischemic limbs of diabetic patients. However, in some instances, the presence of angiogenic factors still fail to promote vascular growth. It has been recently observed that administering certain growth factors provides no added benefit when combined with transmyocardial revascularization. Various systems have been also developed in the past for delivery of these particular drugs or other therapeutic agents to specific target sites including the coronary region. Meanwhile, angiogenic activity has been observed even without the delivery or the presence of any growth factors. More specifically, neovascularization may be initiated during grafting procedures, ischemic conditions or other instances of tissue damage. The delivery of particular drugs and therapeutic agents under the influence of different conditions and stimulus have not provided consistent results in initiating a true angiogenic response.